vue el-tree 默认展开第一个节点的实现代码

<template>
 <section>
  <!-- 机构类型编码表 -->
  <el-row class="toolbar" style="width: 20%;height:600px" align="left">
   <div class='treeClass'>
    <el-tree :data="treeData" :props="defaultProps" @node-click="handleNodeClick"
     highlight-current node-key="id" :default-expanded-keys="treeExpandData">
    </el-tree>
   </div>
  </el-row>
 </section>
</template>
<script>
export default {
  data() {
   return {
    treeData:[], //后台返回的tree树列表
    treeExpandData:[], //自己定义的用于接收tree树id的数组
    provincialCenterId:'',
    defaultProps: {
     children: 'item',
     label: 'name',
    },
    }
  },
   created(){
   this.getEquipmentList()
  },
   methods: {
   // 获取树形结构默认展开节点
   getRoleTreeRootNode(provincialCenterId) {
    this.treeExpandData.push(provincialCenterId)   
    },
   //获取tree树列表
   getEquipmentList: function(params){
    this.listLoading = true
    this.$api.ckApi.treeList({typeTag:true}).then((res)=>{
     if(res.code==200){
      this.treeData = res.resultDownload;
      this.provincialCenterId = this.treeData[0].id //默认展开第一个节点
      this.getRoleTreeRootNode(this.provincialCenterId)
      this.listLoading = false
     }else{
      this.$message.error(res)
     }
    })
   },
   }
</script>